Nonparaxial propagation of ultrashort laser pulses in plasma channels

The propagation characteristics of an ultrashort laser pulse in a preformed plasma channel are analyzed. The plasma channel is assumed to be parabolic and unperturbed by the laser pulse. Solutions to the wave equation beyond the paraxial approximation are derived that include finite pulse length eff ects and group velocity dispersion. When the laser pulse is mismatched with in the channel, betatron oscillations arise in the laser pulse envelope. A finite pulse length leads to a spread in the laser wave number and conseque ntly a spread in betatron wave number. This results in phase mixing and dam ping of the betatron oscillation. The damping distance characterizing the p hase mixing of the betatron oscillation is derived, as is the dispersion di stance characterizing the longitudinal spreading of the pulse. [S1063-651X( 99)04301-9].